It'll vary by make and model, but most mag springs are pretty strong. Unless you're talking about a magazine sitting around untouched, and filled to max capacity for years...I don't think there's much reason for concern.

If it worries you, load it to 80-90% instead. That reduces the tension considerably.

I load my mags just like another poster stated...I leave them 1 or 2 short if I am storing them. I saw where a Glock expert said that it reduces the stress greatly by doing this. Now I just need to figure out how he got to be a Glock expert. I think all you need is a subtitle below your name/picture saying as much.

Good quality steel springs in magazines are not damaged by staying compressed. There was actually a test where a 1911 was found holding a mag loaded in the 1920s. Over 50 years being loaded, shot just fine.

Now, if you will pardon me, I have to go outside and jack up my truck. I don't want the springs on the suspension to stay loaded all the time.

Contemporary, quality magazines produced with equal quality springs will retain their functionality longer than you will.

As stated before, springs are affected by cycles, not by being left fully compressed.

If you were really concerned about your magazine springs being under compression for any length of time, you would need to completely disassemble your mags for storage. This would be the only way the springs could be stored at rest.

Good quality steel springs in magazines are not damaged by staying compressed. There was actually a test where a 1911 was found holding a mag loaded in the 1920s. Over 50 years being loaded, shot just fine.

Now, if you will pardon me, I have to go outside and jack up my truck. I don't want the springs on the suspension to stay loaded all the time.

Not sure how long they can be loaded. I used some loaded mags for my 1911 last Tuesday. They worked fine and I reloaded them three times on the range and they are loaded now. But these mags have been sitting on the shelf, fully loaded for over a year.

I have some Glock mags that have been loaded since 2003 when I moved into this house. Have shot some of them lately but got about 15 more still loaded. Might be a few years before I shoot them since I stopped shooting any of my Glocks months ago.